Dante Chinni is the writer of Politics Counts , which runs every Friday. Mr. Chinni is the author of Our Patchwork Nation, which examines different types of communities across the U.S.

On its face, the Senate’s immigration reform effort seems a bipartisan affair. Four Democratic and four Republican co-sponsors crafted a bill that would fundamentally change immigration policy and offer illegal immigrants a pathway to citizenship.

But the fault lines around the bill are numerous, particularly where the Republican Party is concerned.

This week the conservative Heritage Foundation stirred considerable debate when it released a report suggesting that providing a path to citizenship for illegals could end up costing the country $6.5 trillion. On Tuesday, Republican Sen. Jeff Sessions, who sits on the Judiciary Committee, offered scores of amendments aimed at watering the bill down or derailing it. And at Thursday’s Judiciary Committee meeting, six Republicans voted to put off allowing illegal immigrants to apply to become legal citizens until the border is secure.

Big factors driving the GOP divide in the Senate are some inherent differences in the demographics of the constituents served. You can see them when you look at the bipartisan group of eight senators sponsoring the bill.

The so-called gang of eight senators may come from opposite sides of the aisle, but for the most part they share one common trait: large foreign-born populations back in their home states, according to U.S. Census data that counts both foreign-born citizens and noncitizens. And that commonality separates them from many of their colleagues, especially on the Republican side of the aisle.

Foreign-Born Population and Senate Representation – Averages

Gang of Eight States

DemocraticStates

Republican States

Split States

Total State Average

Foreign-born pop

15%

12.4%

6.7%

6.7%

8.8%

When you look at the numbers that way it easy to see where the Republicans problems are coming from in the Senate.

Immigration in most those gang of eight states – Arizona, Colorado, Florida, Illinois, New Jersey, New York and South Carolina – clearly looks like more of a pressing issue. With an average of 15% of their population foreign born, the “gang of eight” states have more immigrant constituents states represented by Republicans senate delegations and even more that states represented by Democratic delegations.

Yes, there are differences in the gang of eight group. Co-sponsor Sen. Lindsey Graham, for instance, represents South Carolina, which is only 4.7% foreign-born. But he’s the exception. Every other senator in the gang of eight is above average in the number of foreign-born constituents back home and some are far above.

Sen. Marco Rubio, who has led the Republican charge on immigration reform, comes from Florida, where more than 19% of the people are foreign-born. Sen. Charles Schumer, the Democratic primary sponsor of the bill, is from New York, which is 22% foreign-born. Immigrants and the challenges they face are very much a part of everyday in their home states and their constituents.

Click on the image above for the full graphic.

Is it any wonder that those senators, be they Democrats or Republicans, see immigration reform differently than Mr. Sessions, whose home state, Alabama, is only 3.4 foreign-born?

And there are many Republicans in similar situations to Mr. Sessions. Kentucky, home of Sens. Mitch McConnell and Rand Paul, is only 3.2% foreign-born. Mississippi, home of senators Thad Cochran and Roger Wicker, is only 2.2% foreign-born.

There is evidence that the constituents in these different kinds of states also have different feelings about immigration and offering a pathway to citizenship. Politics Counts ran the numbers from a recent Wall Street Journal/NBC poll question on immigration to look at those represented by the gang of eight as well as those represented by only Democratic senators, only Republican senators and those with split delegations.

There is a proposal to allow foreigners who have jobs but are staying illegally in the United States to apply for legal status. Do you strongly favor, somewhat favor, somewhat oppose, or strongly oppose this proposal?

Favor

Oppose

States Represented By Gang of Eight

54%

43%

States with only Democratic Senators

58%

40%

States with only GOP Senators

47%

49%

States with Split Delegations

51%

47%

Those poll numbers from gang of eight states look very similar to Democratic states – with strong numbers favoring a pathway to citizenship – while states represented by Republicans alone opposed that plan, albeit by a small margin.

To be clear, a high number of foreign-born residents in one’s home state does not necessarily equal support for the gang of eight immigration bill.

Overall, however, the data here suggest the on-the-ground differences in immigrant populations will play a role in the Senate debate.

In 19 states less than 5% of the population is foreign-born. In 16 other states more than 10% of the population is foreign-born. Those kinds of numbers seem to generally lead to very different ideas and approaches on immigration.

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